This application claims the priority of Application No. 2002-136171, filed May 10, 2002 in Japan, the subject matter of which is incorporated herein by reference.
This invention relates to a power circuit, and more particularly to, a step-down power circuit, performs DCxe2x80x94DC conversion. Such a step-down power circuit may be called xe2x80x9cswitched capacitor type power circuitxe2x80x9d.
A conventional step-down power circuit is shown in xe2x80x9cNational Semiconductor Co. Ltd., Lm3352 Regulated 200 mA Buck-Boost. Switched-Capacitor DCxe2x80x94DC converter, 1993-3.
The conventional step-down power circuit usually includes voltage-dividing capacitors, smoothing capacitors and switch circuits. In a charging cycle, a voltage-dividing capacitor and a smoothing capacitor are connected between a power supply terminal VDD and a ground terminal GND, so that each of the capacitors is charged to a voltage of VDD/2. In a discharging cycle, a voltage-dividing capacitor and a smoothing capacitor are now connected between an output terminal and the ground terminal GND.
Such charging and discharging cycles are repeated alternately at a high speed, so that an output voltage having a voltage level of VDD/2, which is step-downed, is outputted from the output terminal. According to the above-described power circuit, the output voltage Vo is almost fixed at VDD/2.
Accordingly, an object of the present invention is to provide a power circuit, which can supplies a required or desired output power with a simple structure.
Additional objects, advantages and novel features of the present invention will be set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
According to a first aspect of the present invention, a power circuit includes: a first power node supplying a first level of power; a second power node supplying a second level of power, which is lower than the first level; a first voltage-dividing capacitor, comprising an anode which is capable to be connected to the first power node and a cathode which is capable to be connected to the second power node; a second voltage-dividing capacitor, comprising an anode which is capable to be connected to the first power node and a cathode which is capable to be connected to the second power node; and an output terminal supplying an output voltage in first and second cycles, which are occurred alternately.
The power circuit also includes a control circuit functioning to connect, in the first cycle, the anode of the first voltage dividing capacitor to the first power node, the cathode of the first voltage dividing capacitor to the output terminal and to the anode of the second voltage-dividing capacitor, and the cathode of the second voltage-dividing capacitor to the second power node; and in the second cycle, the anode of the second voltage dividing capacitor to the first power node, the cathode of the second voltage dividing capacitor to the output terminal and to the anode of the first voltage-dividing capacitor, and the cathode of the first voltage-dividing capacitor to the second power node.
According to a second aspect of the present invention, a method includes the steps of providing first and second voltage-dividing capacitors; providing a first power terminal supplying a first level of power and a second power terminal supplying a second level of power, which is lower than the first level; connecting the first and second voltage-dividing capacitors in series between the first and second power terminals in even cycles; and connecting the first and second voltage-dividing capacitors in series between the second and first power terminals in odd cycles, which occur alternately with the even cycles.
According to another aspect of the present invention, a method of power supply, including the following steps:
1) providing first and second voltage-dividing capacitors;
2) providing a first power terminal supplying a first level of power and a second power terminal supplying a second level of power, which is lower than the first level;
3) connecting the first and second voltage-dividing capacitors in series between the first and second power terminals in even cycles; and
4) connecting the first and second voltage-dividing capacitors in series between the second and first power terminals in odd cycles, which occur alternately with the even cycles.
Preferably, the above method further includes the steps of: providing first and second output nodes; and compensating the difference of electric charge between the first output node and the second output node.